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How Moon Phase Watches Work, and Why They're Special

A moon phase watch reminds us that we’re all just spinning through space on this pale blue dot, orbited by a glowing rock, mere cogs in a bigger clockwork.

omega speedmaster coax moonphase gear patrol lead full
Henry Phillips

Timekeeping was born out of man’s desire to make sense of the movement of the sun, the moon and the constellations. When the early horologists graduated from the sundial to gears and hands, one of the important events they tracked was the lunar cycle. This is because although the sun’s arc dictates days and seasons, observing the moon was the first method of telling the passing of months. From new moon to full moon and back again is 29 and a half days, providing a regular cycle that has been the life cycle for any number of things over the centuries, from pagan celebrations to paychecks.

A moon phase watch shows the current phase of the moon as you see it in the sky. As our orbiting pet rock passes across the sky, so too does its miniature version in the watch travel around, displayed in an aperture on the dial. This type of watch is perhaps the most elemental in its graphical representation of the passage of time, as opposed to the more precise and sterile hands and numbers that other complications use. It is a more whimsical and artistic complication, one that is fun to own, linking us with our sky-watching ancestors and a lineage of watchmakers and artisans all at once.

A “moon phase” is the lighted area of the moon that is visible as it travels around the earth. The movement of the Earth and the moon’s position relative to us means that we are constantly seeing a different view. While astronomers have several names for the appearance of the moon throughout its cycle — "waxing gibbous" to "waning crescent" and others in between — there are really only four phases you need to know:

c1 moonglow
Christopher Ward

A “new moon” occurs when the moon and sun are in alignment on the same side of the Earth and thus there is no moon visible to us. As the moon travels through its monthly orbit, more of its surface becomes illuminated by the sun — known poetically as “waxing”. The second phase, known as the “first quarter”, is when the right-hand side of the moon is in the sun’s light. Next comes the “full moon” when the entire surface is lit up. Then it moves to the “last quarter” when the left-hand side is visible — waning — until it finally goes back to a new moon again.

This entire cycle of phases takes 29 and a half days, which is the average length of our calendar month. Given the moon’s regular movement, it is logical then that our modern calendar is tied to the phases of the moon. Thanks to some ancient Roman political and religious fiddling, days were added or subtracted days to certain months, which is why our 12 months aren’t all 29 and a half days. Besides, can you imagine starting a new month at noon on day 30?

The moon has always played a major role in man’s movements and daily existence, from the ebb and flow of tides to religious ceremonies, crop harvests and maritime navigation, which is why it has always been historically important to keep track of its orbit. Though the phases of the Moon were tracked thousands of years ago in crude fashion, the moon phase was commonly found in the more complicated pocket watches in the late 19th and early 20th centuries. When the pocket watch made way for the wristwatch, so too did the moon phase migrate to the wrist. The moon phase really represents the watchmaker’s connection to time itself; it is a sort of miniature version of the gear train that is our universe.

jaquet droz grande seconde moon anthracite
Hodinkee Shop

Behind the dial of a typical moon phase watch is a disc with two identical moons on it. This disc rotates one complete cycle every twenty-nine and a half days, with the waxing and waning face of the moon accounted for by the curved edges of the dial aperture. The moon disc is driven by a 59-tooth gear that is advanced one notch by a mechanical finger every 24 hours, thus corresponding to one full rotation for the entire lunar cycle — almost.

In reality, the moon isn’t this cooperative. The true lunar cycle lasts 29 days, 12 hours and 44 minutes, or 29.53 days. While this accuracy is good enough for the average person, watchmakers are a precise lot and not content with rounding up or down. Being off by .03 days per month means that the entire moon phase cycle will be off by one full day every two years, seven and a half months. To overcome the discrepancy between the measured lunar cycle and the actual moon phases, a more sophisticated mechanism was developed that incorporates a 135-tooth gear to drive the moon disc. This improvement increases the accuracy of the movement so that the moon phase complication will only be off by a day once every 122 years, meaning that your grandson might need to do some adjustment, hopefully remembering your generosity when he does.

Our lives may no longer be tied as closely to the moon’s orbit, just as the wristwatch has largely become an anachronism in this age of smart phones and smartwatches. Which makes it all the more fitting to own a moon phase watch: its timeless charm and whimsical artistry remind us that we’re all just spinning through space on this pale blue dot, orbited by a glowing rock, mere cogs in a bigger clockwork.

9 Great Moonphase Watches

Christopher Ward
Christopher Ward C1 Moonglow
christopherward.com
$1,995.00

Independent British brand Christopher Ward is known for its high bang-for-buck watches, and its C1 Moonphase is an example of one of the most captivating and affordable examples of this complication. Whereas most watchmakers will tuck a moonphase display into a discrete subdial, here it fully occupies half the dial. Even cooler is that it's drenched in lume to glow brightly, while the lower half of the dial is tinted sapphire so the other side of the moon phase disk is also visible for a striking look.

Frederique Constant Geneve
Frederique Constant Slimline Moonphase Manufacture
frederiqueconstant.com
$3,995.00

Frederique Constant hangs its hat on building conservatively styled dress watches with complications and in-house movements at highly competitive prices. This alone makes its Slimline Moonphase Manufacture attractive, but as its name indicates, this is also a reasonably thin watch at 11.3mm thick and 42mm in diameter. Taking the popular and intuitive approach of combining the date and moon phase in a subdial at 6 o'clock, it's powered by the brand's own FC-705 automatic movement.

Courtesy
Montblanc Star Legacy Moonphase
montblanc.com
$4,300.00

If you want a traditional take on the moonphase, Monblanc feels like the right kind of brand to do it. Housed in their Star Legacy collection, this is no off-the-shelf design and shows that the brand’s conservative side doesn’t lack personality. It includes a Sellita SW200 automatic movement with a moonphase module by Dubois-Depraz, a fascinating guilloché pattern emanating from the brand’s star logo, and it all comes in a 42mm case made of sterling silver.

Ochs und Junior
Ochs und Junior Moon Phase
ochsundjunior.swiss
$7,400.00

Ochs und Junior prides itself on building “rigorously simple watches,” and its Moon Phase is a testament to this philosophy. Built upon the ubiquitous ETA 2824-2 automatic movement, the moon phase function looks overly simplistic but is actually the most accurate one available; in 3,478.27 years, it will only be off by one day. The watch’s dial and case are typically industrial, bordering on the elemental, but the latest versions come alive with strikingly vibrant colors.

Courtesy
Cartier Ballon Bleu Moonphase
cartier.com
$7,700.00

Cartier might be associated with Roman numerals and formal styles, but their designs are anything but boring. With a highly unusual interpretation of the moon phase complication, the display's placement at 9 o’clock is unexpected but maintains a sense of balance with the unique crown design characteristic of the Ballon Bleu collection. Powered by an automatic movement, its 37mm case with short lugs should be highly wearable for a range of wrist sizes.

Hodinkee Shop
Omega Speedmaster Moonwatch Co-Axial Master Chronometer Moonphase Chronograph
hodinkee.com
$10,600.00

The Speedmaster Professional was the first watch worn on the moon, so it’s fitting that Omega fitted a version of its iconic chronograph with a moon phase complication. The brilliant blue dial is matched to a moon disc, and the date function is integrated into the 9 o'clock seconds sub dial. These differences don't diminish the watch’s legendary utility; it's powered by a METAS-certified Master Chronometer automatic movement and is 44.25mm in width. We think NASA would still approve.

Hodinkee Shop
Jaquet Droz Grande Seconde Moon Anthracite
hodinkee.com
$15,200.00

Jaquet Droz's signature, elegant figure-eight dial is only elevated by a moonphase that fits right into the overall design. The Grande Seconde Moon Anthracite is descriptively named with the larger subdial housing a sweeping seconds hand, date display and moon phase, while the hours and minutes are indicated by the smaller dial above it. The blue hands and moon phase disk contrast brilliantly against the sandblasted anthracite dial, and it's all powered by an in-house movement in a 43mm steel case.

Courtesy
Arnold & Son Luna Magna
arnoldandson.com
$43,900.00

Arnold & Son has long stood out in the moon phase game for its Perpetual Moon watch which did the whole giant moon phase display well before others (like Christopher Ward above). It’s newest moon phase watch, however, takes a totally different approach, with the phase of the moon displayed via an actual orb which is half white marble and half aventurine glass. You can even see the other side of the orb through the case back, along with a secondary display for a more precise reading of the current phase as well as the beautiful in-house, manually wound movement.

Courtesy
Moser Endeavour Perpetual Moon
h-moser.com
$43,900.00

Moser’s always got a statement to make or artistic concept that seems to invite interpretation. Here, an aventurine dial employs its natural resemblance to a deep blue, starry sky. The view is unobstructed by indices for reading the time, leaving only a pair of hands and a moon phase display at 6 o’clock. The moon phase complication is regularly described as “poetic” and “romantic,” but here it feels more appropriate a word choice than ever. As long as you keep the manually wound movement ticking, the in-house movement promises that the phases of the moon won’t need adjustment for 1,027 years.

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